This invention relates to a system and methods for characterizing the pressure, movement and temperature of a fluid and for viewing the flow pattern of the fluid within a testing cell, and more particularly, but not by way of limitation, a fiber optic system and methods for measuring the pressure of the fluid, a laser system and methods for measuring movement of the fluid, a temperature sensing system and methods for estimating temperature of the fluid, and a fiber optic system and methods for viewing the flow of the fluid within a fluid testing cell for testing the behavior and characteristics of fluids under high pressures.
Fracturing fluids are used in natural gas recovery technology to increase the permeability of underground gas-laden rock. Increasing the rock permeability increases the amount of gas which can be recovered from an underground gas reservoir. The increase in permeability is obtained when fracturing fluids are pumped into the bore of the well under high pressures, thereby causing rock surrounding the well bore to fracture. These fractures may be hundreds of feet in length and, due to the great underground pressures, have a tendency to close. To reduce this tendency, a proppant such as sand is pumped along with the fluid into the bore. The proppant enters and lodges within the fracture and prevents the fracture from closing.
It has long been a goal of industry to simulate in the laboratory the shear history experienced by these fluids in the field environment. Fluids in such environments are subject to numerous and complex conditions. It is important to be able to model the rheological properties of the fluids under such conditions to be able to predict their behaviors. However, fluid models, in order to be designed and to be improved to better reflect behaviors under in-situ conditions, should be subject to simulation and experimental verification.
As an example, in order to exploit the extremely low-permeability gas reservoirs indigenous to the Tight Sands Regions of the U.S., fluid rheological and fracture propagation models need to be developed such that predictions based on these models will carry a much higher level of confidence than is currently available with existing technology.
In order to develop accurate models, the effects of many variables on the rheology of fracturing fluids with and without proppant must be thoroughly investigated. Among the variables which must be studied are temperature, fracture shear rate, fluid leak off volume, roughness of fracture walls, viscoelastic properties of gels, pressure time, proppant settling rates, proppant concentration, proppant size, proppant density and fracture dimension.
There is currently no experimental tool which can be effectively used to simulate the in-situ conditions to which fracturing fluids are subjected so these factors can be investigated.
Rheological studies on fluids flowing around objects have traditionally been performed on Hele-Shaw cells which are comprised of narrowly-separated parallel plates which allow a flow of fluid between them. At least one of the plates should be transparent to enable the viewing of the fluid flow. However, there is no system in the current rheological technology which (1) simulates the porous rock facing which exists within the well fracture, (2) allows changes in pressure, strain and shear applied to the hydraulic fluid during experimentation and (3) allows accurate measurement of important fluid parameters and properties such as velocity, pressure, and flow pattern.